Patent GB-292602-A (GB)
Title: Improvements in or relating to photographic cameras
IPC: G03B13/18
Filed: 1928-06-18
Abstract: 292,602. Tonnies, H. F. June 24, 1927, [Convention date]. Range-finders.-A photographic camera is provided with a range-finder of the short home base coincidence type having parallel inclined mirror surfaces at the ends of the base and two lenses, preferably of cylindrical form, of equal local length but opposite sign, arranged one behind the other in the optical path of the rays through the device, one of the lenses being displaceable at right-angles to its optical axis for the purpose of making the coincidence adjustment. According to the invention, the lenses 6, 7 are placed in front of the optical base formed by the mirrors 4, 5, and the adjustable lens 6 is displaceable parallel to the base until an eye, looking into the observing mirror 21, sees coincidence between the beam CD, Fig. 2, which passes through the optical system and the beam ED which passes directly to the mirror 21 over the mirror 5. The displacement of the lens 7 is preferably effected by means associated with the extension slide carrying the objective carriage of the camera, so that the camera is automatically focused on an object by racking out the objective until coincidence is observed in the mirror 21. As shown in plan in Fig. 5, the parts are mounted in a casing 17 which forms the lower horizontal part of the lens carriage, and is divided by partitions 25, 26 into chambers housing respectively the bases 6, 7 and a prism 3 whose end faces constitute the mirrors 4, 5. The lens 7 is mounted in a slide 29 displaceable parallel to the base 4-5 against the tension of a spring 9 by a chain 10, Fig. 2, passing round a roller 11 and connected to a lever 12 which rests, when the camera is extended, against a stop 14. To effect the initial adjustment of the device, the objective carriage is drawn out until it is arrested in the infinity position, in which the lever 12 rests against the stop 14. If the mirror 21 does not exhibit coincidence, the front lens 7 is displaced, parallel to the base 4-5, against the action of a spring 32, by an adjusting screw 35 until coincidence is observed, and the device is then correct for the infinity setting. The objective carriage is now moved forward to focus accurately a near object, and during this movement the fixed stop 14 turns the lever 12 and so displaces the lens 6. If the mirror 21 again fails to exhibit coincidence, the set screw 14a is loosened, the stop 14 is rocked about its pivot 14b until coincidence is observed, and the screw 14a is tightened; the device is then correctly set for focusing near objects also. An object at any distance may be then accurately focused by sighting the object in the mirror 21, and moving the camera lens forward until the sections of the object seen in the mirror 21 coincide. In a modification, the device is mounted on the side wall 46, Fig. 6, of the camera and the mirror surface 5 is viewed directly from the rear. The chain 10 controlling the displacement of the lens 6 passes through a tube 45 in the wall 46 and is attached to plate 43 pivotally mounted on the extension slide 39 supporting the objective carriage 18. As the extension slide 39 is moved forward for focusing, A pin 57 on the plate 43 engages a cam surface 59 fixed to the baseboard 40 at an angle to the direction of movement of the slide 39, causing the plate 43 to turn on its pivot and thereby displace the lens 6. The initial setting of this plate 43 or an adjustment of the lens 7 parallel to the base 4-5, when the objective is focused at infinity; and by a displacement of the cam 59 parallel to the axis of the objective 1 when this is focused on a near object, both adjustments being continued until coincidence is observed in the mirror 5.